On the rank of the distance matrix of graphs

TL;DR

This paper investigates the rank of distance matrices in graphs, proving finiteness for each rank, classifying low-rank cases, and analyzing nullity bounds within specific graph families.

Contribution

It establishes finiteness results for graphs with fixed distance matrix rank, classifies graphs with rank 2 and 3, and explores nullity bounds in trivially perfect and threshold graphs.

Findings

Finiteness of graphs with a given distance matrix rank using Ramsey's theorem.

Complete classification of graphs with distance matrices of rank 2 and 3.

Nullity bounds established for trivially perfect and threshold graphs.

Abstract

Let $G$ be a connected graph with $V(G)=\{v_1,\ldots,v_n\}$. The $(i,j)$-entry of the distance matrix $D(G)$ of $G$ is the distance between $v_i$ and $v_j$. In this article, using the well-known Ramsey's theorem, we prove that for each integer $k\ge 2$, there is a finite amount of graphs whose distance matrices have rank $k$. We exhibit the list of graphs with distance matrices of rank $2$ and $3$. Besides, we study the rank of the distance matrices of graphs belonging to a family of graphs with their diameters at most two, the trivially perfect graphs. We show that for each $\eta\ge 1$ there exists a trivially perfect graph with nullity $\eta$. We also show that for threshold graphs, which are a subfamily of the family of trivially perfect graphs, the nullity is bounded by one.